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  <title>播下随机数发生器种子</title>

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</div><hr /><div id="function.srand" class="refentry">
   <div class="refnamediv">
    <h1 class="refname">srand</h1>
    <p class="verinfo">(PHP 4, PHP 5)</p><p class="refpurpose"><span class="refname">srand</span> &mdash; <span class="dc-title">播下随机数发生器种子</span></p>

   </div>
 <div class="refsect1 description" id="refsect1-function.srand-description">
  <h3 class="title">说明</h3>
   <div class="methodsynopsis dc-description">
    <span class="type"><span class="type void">void</span></span> <span class="methodname"><strong>srand</strong></span>
     ([ <span class="methodparam"><span class="type">int</span> <code class="parameter">$seed</code></span>
   ] )</div>

    <p class="para rdfs-comment">
     用 <em><code class="parameter">seed</code></em> 播下随机数发生器种子。<em><code class="parameter">seed</code></em> 参数没有给出时，会被设为随时数。
    </p>
  
  <blockquote class="note"><p><strong class="note">Note</strong>: <span class="simpara">自 PHP 4.2.0 起，不再需要用
<span class="function"><strong>srand()</strong></span> 或 <span class="function"><a href="function.mt-srand.html" class="function">mt_srand()</a></span>
给随机数发生器播种 ，因为现在是由系统自动完成的。</span></p></blockquote>
  
   </div>

 <div class="refsect1 parameters" id="refsect1-function.srand-parameters">
  <h3 class="title">参数</h3>
  <p class="para">
   <dl>

    
     <dt>
<em><code class="parameter">seed</code></em></dt>

     <dd>

      <p class="para">
       可选的种子值
      </p>
     </dd>

    
   </dl>

  </p>
 </div>


 <div class="refsect1 returnvalues" id="refsect1-function.srand-returnvalues">
  <h3 class="title">返回值</h3>
  <p class="para">
   没有返回值。
  </p>
 </div>


 <div class="refsect1 changelog" id="refsect1-function.srand-changelog">
  <h3 class="title">更新日志</h3>
  <p class="para">
   <table class="doctable informaltable">
    
     <thead>
      <tr>
       <th>版本</th>
       <th>说明</th>
      </tr>

     </thead>

     <tbody class="tbody">
      <tr>
       <td>Since 4.2.0</td>
       <td>
        <em><code class="parameter">seed</code></em>  成为可选，省略时会默认使用随机值。
       </td>
      </tr>

     </tbody>
    
   </table>

  </p>
 </div>

 <div class="refsect1 examples" id="refsect1-function.srand-examples">
  <h3 class="title">范例</h3>
  <p class="para">
   <div class="example" id="example-3386">
    <p><strong>Example #1 <span class="function"><strong>srand()</strong></span> 例子</strong></p>
    <div class="example-contents">
<div class="phpcode"><code><span style="color: #000000">
<span style="color: #0000BB">&lt;?php<br /></span><span style="color: #FF8000">//&nbsp;seed&nbsp;with&nbsp;microseconds<br /></span><span style="color: #007700">function&nbsp;</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">()<br />{<br />&nbsp;&nbsp;list(</span><span style="color: #0000BB">$usec</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">$sec</span><span style="color: #007700">)&nbsp;=&nbsp;</span><span style="color: #0000BB">explode</span><span style="color: #007700">(</span><span style="color: #DD0000">'&nbsp;'</span><span style="color: #007700">,&nbsp;</span><span style="color: #0000BB">microtime</span><span style="color: #007700">());<br />&nbsp;&nbsp;return&nbsp;(float)&nbsp;</span><span style="color: #0000BB">$sec&nbsp;</span><span style="color: #007700">+&nbsp;((float)&nbsp;</span><span style="color: #0000BB">$usec&nbsp;</span><span style="color: #007700">*&nbsp;</span><span style="color: #0000BB">100000</span><span style="color: #007700">);<br />}<br /></span><span style="color: #0000BB">srand</span><span style="color: #007700">(</span><span style="color: #0000BB">make_seed</span><span style="color: #007700">());<br /></span><span style="color: #0000BB">$randval&nbsp;</span><span style="color: #007700">=&nbsp;</span><span style="color: #0000BB">rand</span><span style="color: #007700">();<br /></span><span style="color: #0000BB">?&gt;</span>
</span>
</code></div>
    </div>

   </div>
  </p>
 </div>

 <div class="refsect1 seealso" id="refsect1-function.srand-seealso">
  <h3 class="title">参见</h3>
  <p class="para">
   <ul class="simplelist">
    <li class="member"><span class="function"><a href="function.rand.html" class="function" rel="rdfs-seeAlso">rand()</a> - 产生一个随机整数</span></li>
    <li class="member"><span class="function"><a href="function.getrandmax.html" class="function" rel="rdfs-seeAlso">getrandmax()</a> - 显示随机数最大的可能值</span></li>
    <li class="member"><span class="function"><a href="function.mt-srand.html" class="function" rel="rdfs-seeAlso">mt_srand()</a> - 播下一个更好的随机数发生器种子</span></li>
   </ul>
  </p>
 </div>

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